1. Field of Invention
This invention relates to methods and apparatus that automatically identify the marking process used to form an image on a substrate. More particularly, this invention relates to methods and apparatus for identifying the marking process based on spatial characteristics of the image.
2. Description of Related Art
In order to accurately calibrate a color scanner that scans an image carried on a substrate, a different calibration transformation is required depending on the marking process and materials used to form the image on the substrate. For example, the calibration transformation that is used to calibrate the scanner for a photographic image is different from the calibration transformation that is used to calibrate the scanner for an ink-jet-printed image, which is in turn different from the calibration transformation that is used to calibrate the scanner for a xerographically-formed image.
Typically, a user wishing to scan an image must determine the marking process used to form the image, and then manually identify the marking process (e.g., photographic, lithographic, ink-jet, line-on-line xerographic or rotated-screen xerographic) to the scanner so that an appropriate calibration can be made.
An approach to automatically identifying the marking process using additional spectral information from the scanned material obtained through additional spectral channels is described in co-pending application Ser. No. 09/047,453, assigned to Xerox Corporation. The techniques described in that application require additional hardware, such as an optical system, to determine the marking process.
It would be advantageous to have methods and apparatus that automatically identify the marking process and materials without requiring additional hardware.
Images carried on substrates exhibit unique spatial characteristics depending on the marking process used to form these images. This invention provides methods and apparatus that automatically identify a marking process based on at least one spatial characteristic of the marked image.
In one exemplary embodiment of the systems and methods of this invention, the spatial characteristic is identified using a power spectrum of the image.
In other exemplary embodiments of the systems and methods of this invention, the power spectrum is analyzed according to the existence, position, and/or color of spectral peaks in the power spectrum.
In other exemplary embodiments of the systems and methods of this invention, the power spectrum is analyzed according to the existence or absence of abnormally high energy in the high frequencies in the power spectrum.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of preferred embodiments.